Fuel pumps and fuel dispensers are known in the art. A fuel pump includes a pump located within its housing for extracting fuel from a fuel source, as well as meters for measuring fuel flow and switches and valves for controlling fuel flow. A fuel dispenser, in contrast, is connected to a source of fuel which contains its own pump, typically an underground storage tank (UST) with a submersible turbine pump (STP). Thus, a fuel dispenser does not typically require that a pump be housed in the unit itself. Instead, the dispenser housing contains the appropriate meters, switches and valves for controlling fuel flow supplied to it under pressure. As used herein, the term “fuel dispenser” shall include both fuel pumps and fuel dispensers, unless the context clearly indicates otherwise.
Fuel dispensers are designed in a variety of different configurations. A common type of fuel dispenser, often called a “lane-oriented” dispenser, has one or more fuel dispensing nozzles on each side of the unit. A lane-oriented multiproduct fuel dispenser typically has two or more fuel dispensing nozzles on each side of the unit. Each of the nozzles on each side of the unit is typically used to dispense a particular grade (e.g., octane level) of fuel. Alternatively, a single nozzle may be provided for dispensing multiple grades of fuel depending on the customer's selection. Each side of the unit generally includes a display for displaying the amount and cost of the fuel dispensed, and can also include credit or debit card verification and cash acceptance mechanisms.
A variety of different meters have been used in prior art fuel dispensers. Typically, either positive displacement meters or inferential meters have been used for this purpose. For a variety of reasons, fuel volume or flow rate measurement technologies are typically limited in their measurement accuracies across a finite range of flow rates. Additionally, measurement technologies may be limited in their maximum flow rates at the desired, restricted-to and/or otherwise realistic operating pressures by internal restrictions or fluidic impedances including but not limited to bore, port or other orifice size. Moreover, these measurement technologies require periodic recalibration and/or special filters.
Flow meters utilizing the Coriolis Effect to measure the mass flow rate of a fluid are also known. Generally, in such Coriolis meters an electromechanical actuator forces one or more fluid-filled flow conduits to vibrate in a prescribed oscillatory bending-mode of vibration. When the process-fluid is flowing, the combination of fluid motion and conduit vibration causes inertial forces which deflect the conduits away from their normal paths of vibration proportionally related to mass flow rate. Motion of the conduit is measured at specific locations along its length and this information is used to determine mass flow. Detailed information on the structure and operation of traditional Coriolis flow meters is disclosed in U.S. Pat. Nos. 7,287,438 and 7,472,606, both of which are incorporated herein by reference in their entireties for all purposes.
Coriolis flow meters utilize the acceleration effects that govern a mass moving relative to a noninertial, or rotating, frame of reference. For example, consider a fluid particle moving with a velocity v in a fluid stream in a conduit where the conduit is oscillated about an axis perpendicular its centerline with an angular velocity Ω. To an observer in the noninertial frame of reference, the particle appears to accelerate. The particle's acceleration, ap, is given by 2·Ω×v. Thus, the apparent force, Fc, exerted on the particle is:Fc=mp·ap=2·mpΩx v where mp is the particle's mass and x is the vector cross product operator. The Coriolis force acts in a direction perpendicular to both the particle's linear and angular velocities. Because the force is proportional to the particle's mass and velocity, measurement of the force's effect on the conduit allows the mass flow rate of the fluid to be determined.
Current Coriolis mass flow technology has several desirable characteristics over positive displacement and inferential flow meters. For instance, Coriolis meters are highly accurate, they are not subject to wear or meter drift because they lack internal moving parts, they can measure flow in forward and backward directions, and they measure fluid mass directly. Some implementations also measure fluid density directly.
However, although Coriolis meters have been widely used in some industries, they have not been widely adopted in the fuel dispensing industry because of several drawbacks. For example, current implementations are expensive and complex. Limits of current Coriolis meters may also constrain the diameter size, thickness, and/or overall geometry of a flow conduit.
Therefore, room remains in the flow measurement art for a flow meter that utilizes the Coriolis Effect to achieve a highly accurate measurement of mass flow while overcoming the above difficulties. In particular, a flow meter that does not require excitation of the flow conduit could have a less complex geometry, fewer moving parts, and be more readily implemented in a flow to be measured.